Jlj> 



CENTRAL AFRICAN SUB-REGION 



Fig. 217. — ('ulinnnn 

 flammea Mull , 

 Piinces I. 



not yet been well explored. Tomostclc, a genus allied to 

 Streptostele, is peculiar, and Pseudachatinft attains its maxiniuni. 

 St. Thomas and Princes. Is., in the Gulf of 

 Guinea, are well known. Princes I. has 22 

 species, 14 peculiar, and 2 common to 8t. Thomas 

 only, one of the latter being the great sinistral 

 Achatina hicarinata Chem. The remarkable 

 genus Columna (Fig. 217) is peculiar, and 

 Strcidostele (4 sp.) attains its maximum. Peculiar 

 to St. Thomas are Pyrgina, a turreted form of 

 Strnogyra ; Thyroijhorella, a sinistral form of 

 Zonites ; and AtopococJilis, a large bulimoid 

 shell, wdiose .true relationships are not yet known. 

 Homorus, a group of Achatina with an elongated 

 S})ire, occurring also in the Angola District and 

 on the east coast, has 4 species. No fresh-water 

 species have as yet been discovered in either of 

 the islands. 



The Angola and Benguela District, extend- 

 ing from the Congo to the Cunene R, probably belongs to the 

 A^^est African Sub-region, but until its fauna is better known 

 it is advisalile to consider it apart. Achatina continues 

 abundant, but the other characteristic West African forms 

 {Pseudachatina, Streptostele, Perideris) diminish or are absent 

 altogether. No Helix and only 1 Cyelophorus occur. 



Ovariipo, Daniara, and Great Namaqualand, lying Ijetween 

 the Cuniene and Orange rivers, seem to form a transition 

 district between the West and South African faunas. Helix 

 reappears, while the characteristic West African genera are 

 almost entirely wanting. 



{c) The East African Province extends from about Delagoa 

 Bay to the Al)yssinian shores of the Ked Sea. In general out- 

 line the province consists of a flat marshy district, extending 

 inland for many miles from the sea; this is succeeded by rising 

 ground, which eventually becomes a high table -land, often 

 desolate and arid, whose line of slope lies parallel to the trend of 

 the coast. The Mollusca are little known, and have only been 

 studied in isolated districts, usually from the discoveries of 

 exploring expeditions. 



The Mozambicpue District, from Delagoa Bay to Cape Delgado, 



